Treatment of electrical apparatus



Dec. 31, 1940. R. T. REARDON TREATMENT OF ELECTRICAL APPARATUS FiledSept. 20', 1938 Inventor: Robert T. Rear-don, by x) His Attorney.

, Patented Dec. 31, 1940 UNITED STATES TREATMENT OF ELECTRICAL APPARATUSRobert T. Real-don, Fort Wayne, Ind., assignmto General ElectricCompany, a corporation of New York Application September 20, 1938,Serial No. 230,839

3 Claims.

The present invention relates to electric apparatus and moreparticularly to the production of assemblies comprising magnetic coresfor such apparatus.

5 This application is a continuation-in-part of my co-pendingapplication Serial No. 127,405, filed February 24, 1937, and assigned tothe same assignee as the present invention.

In manufacturing certain types of electric equipment, as for examplestators of motors, the general practice heretofore usually has been asfollows:

Thin sheet or strip ferromagnetic material, as for example siliconsteel, was stamped to form stampings or punchings of the desired sizeand shape. These punchings, stacked loosely in trays or boxes, wereannealed in an inert or reducing atmosphere or as described in myaboveidentified application. This annealing treatment 30 removed thestresses and strains set up in the steel by the punching operation andimproved its magnetic properties, However, many of the annealedpunchings would be distorted due to unequal expansion and contractionduring annealing and cooling, or by reason of settling or shifting inthe annealing trays, or for other reasons. Hence in assembling punchingsinto the shell of a stator they had to be clamped under substantialpressure to flatten the distorted members of a the stack. This clampingset up further stresses and strains in the annealed laminations andobviated a substantial amount, in certain cases almost all, of theimprovement in magnetic properties attained by annealing. Moreparticularly,

the magnetizing current is greatly increased at a definite operatingdensity, the permeability reduced, and the hysteresis loss increased. Toproduce a motor which would meet a particular operating specification,it was therefore neces- O sary either to use more copper (ampere turns),or more ferromagnetic metal or a higher quality and more costly metalfor the magnetic core than would be required if the detrimental effectresulting from clamping the annealed laminations and fitting them intothe stator structure could be avoided.

As pointed out in my above-identified co-pending application Serial No.127,405, steel laminations such as used in electric motors may be as- 50sembled in proper position in the iron shell of the motor and the entireassembly including the iron shell then heat treated as thereindescribed, More particularly, by the method of that application theassembly is heated first in an oxidizing 5 atmosphere to form a tightlyadhering insulating oxide film on the laminations and then in anatmosphere containing a reducing but non-carburizing gas, specificallyhydrogen, to prevent the oxide-coated laminations from adhering to eachother, or from becoming highly oxidized at 5 high temperature desirablein developing the best magnetic properties. I

In accordance with the present invention punchings of ferromagneticmaterial are assembled in the form of their ultimate use in electric 10apparatus. Specifically, punchings of such material in parallel,contacting relationship are firmly positioned within a tubular or othercasing adapted to receive the same, for example, within the conventionalshell of a stationary member 15 (stator) of a dynamo-electric machine.The resulting assembly is heat treated at atemperature and for a periodof time sufficient to improve in situ the magnetic properties of thepunchings but insufiicient to cause appreciable distortion of theassembly. During this heat treatment the assembly is surrounded by agaseous atmosphere hereafter more particularly identified.

The novel features which characterize my invention are set forth in theappended claims. 5 The invention itself will be understood most readilyfrom the following more detailed description when considered inconnection with the accompanying drawing wherein Figs. 1 to 4,inclusive, are illustrative of steps employed in producing assembliesembodying my invention; and

Fig. 5 is a perspective view of a wound stator produced in accordancewith the invention.

In carrying my invention into effect hot or cold rolled, mill annealedor semi-mill annealed, or other suitably treated sheet or strip iron orsteel adapted for use in magnetic structures is punched or stamped in adesired manner. For example,

the sheet material may be punched to form a punching I (Fig. 1), whichin turn may be punched to form a slotted punching or lamination 2 (Fig.2), a plurality of which are shown .(Figs. 2 and 5) assembled togetherto form a magnetic core 3. The assembled slotted laminations areclamped, riveted or otherwise joined into the form in which they are tobe used in electric apparatus. For instance, a wrapping 4 (Figs. 3 and5) of sheet iron orother suitable sheet metal may be placed about thecore 3 between the laminae and the formation of a continuous,homogeneous, tightly adhering insulating oxidefilm on the surfacesthereof.

The assembly 6, which is shown in Fig. 4 within. a suitable furnace l,is therein heated in a suitable gaseous atmosphere, specifically oneobas, for example, up to 5%. of such gases, if any, will be present.

tained by the combustion of hydrocarbon-containing material in adeficiency of air and com sisting mainly of nitrogen, carbon monoxide,carbon dioxide, hydrogen and water vapor. The relative proportions ofcarbon monoxide, carbon dioxide, hydrogen and water vapor are such thatthe gaseous atmosphere, at least at the maximum heat-treatingtemperature, is non-oxidizing. Ordinarily, the gaseous atmosphere whichenvelops the assembly during the heat treatment to improve in situ themagnetic properties of the laminations has, at normal temperature,substantially the following composition:

Per cent by volume Carbon monoxide 3to 12 Carbon dioxide 3to Hydrogen3to 25 Water vapor 0.8 to 3.5

Nitrogen, sometimes also a small amount of hydrocarbon gases such asmethane Remainder In all cases the relative proportions of componentsare such that, at least at the maximum heat-treating temperature, thegaseous atmosphere is non-oxidizing (inert or reducing) and, usually, isreducing. Hydrocarbon gases such as methane have no deleterious effectother than that of a diluent when present in small amount Usually lessthan 1% Any suitable apparatus may be used for producing the envelopinggaseous atmosphere, for example apparatus such as described in MarshallPatent No. 2,085,597 and in Haskell Patent No. 2,085,584, both of whichpatents are assigned to the same assignee as the present invention.

The heat treatment can be carried out in a batch-type furnace or in asemi-continuous or continuous furnace. If the batch method is employed,the assemblies should be stacked on racks designed to minimize thepossibility of distortion of the individual assembly during heattreatment. Advantageously the stacked assemblies are covered with a boxor drum formed of suitable alloy and the air about the coveredassemblies is displaced with an inert or reducing gas. Covering the loadcharged to the furnace with a drum is not absolutely necessary, but ifnot used the heattreated assemblies upon removal from the furnace shouldbe inserted promptly under a drum or other suitable structure forcooling.

The furnace previously has been brought to the desired heat-treatingtemperature, for example a temperature of approximately 800 to 860 C.when the assemblies comprise magnetic cores formed of silicon steellaminations. The racks (preferably covered) with the assemblies thereonare charged into the preheated furnace, the atmosphere thereincomprising the above gaseous mixture. The temperature of the furnaceatmosphere drops to 550 to 650 C., requiring about 3 hours to reach 800to 860 C. again. The charge is held for an additional hour at thishigher temperature. The covered assemblies are removed from the furnace,and the above-described gaseous composition is maintained (or a furtheramount may be introduced) under the cover for another hour, during whichtime the assemblies cool to an average temperature of about 600 to 700C. The assemblies are cooled further under cover, discontinuing theintroduction of gas if used, for another'2 to 3 hours, or longer ifdesired. Ordinarily they are cooled under cover to a temperature of theorder of 275 to 475 C. before exposure to the air. By cooling undercover excessive oxidation of the assemblies is avoided. Further, shockchilling of the top and side assemblies of the load is obviated. Suchchilling is to be'avoided, since it causes rapid contraction of themetal, sets up strains in the laminations, distorts the parts, andresults in loose assemblies.

Preferably the assemblies are continuously heat treated. A typical cyclein such case is to bring the work from room temperature (about to C.) toheat-treating temperature in approximately 1% hours, maintain it at suchtemperature for approximately hour, followed by cooling to about 275 to475 C. over a period of approximately 2 hours before exposure to theair. During such heating and cooling the assemblies are enveloped by theabove-described gaseous atmosphere comprising carbon monoxide, carbondioxide, hydrogen and water vapor in suitable proportions. Relativelyslow cooling,'whether the assembly is heat-treated by batch,semi-continuous or continuous methods, is important in obtainingheat-treated assemblies with tightly fitting cores.

It will be understood, of course, that the particular temperatures used,and the particular rates of heating and cooling employed, will dependupon the particular assemblies processed and the particular metals ofwhich they are composed. However, in annealing ordinary magneticstructures in situ the maximum annealing temperature usually will bewithin the range of 650 to 1100 C.

The heat-treated assemblies are fabricated into electric apparatus. Fig.5 shows by way of illustration a wound stator 8, the shell and magneticcore of which were heat treated as an assembly in accordance with thisinvention.

The magnetic cores of assemblies which have been heat treated as hereindescribed show higher permeability and reduced hysteresis losses ascompared with cores formed of punchings similarly annealed prior toassembly. If the laminations comprising the core initially had noinsulating oxide film thereon or were incompletely or non-uniformlycoated with oxide, the described treatment causes a continuous,homogeneous, integral electrically insulating oxide film or coating tobe formed on the surfaces of the laminations while the work is reachingthe maximum heat-treating temperature and in cooling from suchtemperature to normal temperature. This insulating film reduces eddy andcirculating current losses during use of apparatus comprising theassemblies of: this invention. By properly proportioning the componentsof the gaseous mixture, fusion or sticking together of the oxidecoatedlam'inations during heating and cooling is prevented. Further, a tightlyadhering oxide film is formed on the edges of the laminae, including theedges adjacent the iron'shell, as well as on the shell itself. Excessiveoxidation of the iron shell and of the laminations is avoided. Hencemechanical cleaning of the shell, as by sand blasting, machining,bufling, etc., to remove scale is not necessary. No loose oxide or scaleis formed. This is a matter of considerable importance, particularlywhen the assemblies are to be used in the construction of hermeticallysealed refrigerator motors. The core is not loosened in the shell by thedescribed treatment, but fits tightly therein as before heat treatment.

By heat treating assemblies comprising magnetic cores formed of suitablyarranged punchings of ferromagnetic material to anneal in situ thepunchings; that is to anneal the punchings to improve their magneticproperties while they are in the form of their ultimate use in electricapparatus, marked savings in manufacturing costs and substantialimprovement in magnetic properties result. Specifically, a lesser amountof copper or of core material, or of both, is required, or a less costlyferromagnetic material can be used, to obtain practically the samepermeability and hysteresis loss values shown by magnetic cores formedof punchings of the same dimensions and composition, which punchings areannealed in unassembled state under similar time-temperature conditionsand subsequently assembled to form a magnetic core. Or, other conditionsbeing the same, for the same kind and amount of ferromagnetic materialassembled in core form into apparatus, substantially betterelectro-magnetic values (higher permeability and lower hysteresislosses) are obtained by practicing the method of this invention incomparison with the method above described.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. The method which comprises the steps of assembling punchings offerromagnetic material in the form of their ultimate use in electricapparatus, heat treating the assembly at a temperature and for a periodof time sufllcient to improve in situ the magnetic properties of thepunchings but insuflicient to cause appreciable distortion of theassembly, and enveloping the assembly during the said heat treatingoperation with an enveloping gaseous atmosphere containing carbonmonoxide, carbon dioxide, hydrogen and water vapor so proportioned thatthe said atmosphere, at least at the maximum temperature of treatment,is non-oxidizing and prevents the punchings from sticking togetherduring the heat treatment, and at lower temperatures is 50 material.

2. The method which comprises the steps of assembling punchings offerromagnetic material in the form of their ultimate use in electricapparatus, subjecting the assembly to heat treatment suihcient toimprove in situ the magnetic properties of the punchings but insuihcientto cause appreciable distortion of the assembly, cooling theheat-treated assembly, and surrounding the assembly during heating andcooling with an enveloping gaseous atmosphere capable of preventing thepunchings from sticking together during the heat treatment, saidatmosphere being obtained by the combustion of hydrocarbon-containingmaterial in a deficiency of air and containing, by volume, from 3 to 12per cent carbon monoxide, from 3 to 10 per cent carbon dioxide, from 3to 25 per cent hydrogen and from 0.8 to 3.5 per cent water vapor, therelative proportions ofthe said components being such that at themaximum heat-treating temperature the said gaseous atmosphere isnon-oxidizing and at lower temperatures the said gaseous atmospherecauses the formation of a continuous, homogeneous, integral,electrically insulating oxide coating on said assembly.

3. The method of forming a stationary member of a dynamo-electricmachine which includes the steps of firmly positioning punchings offerromagnetic material adapted to have formed thereon a continuous,homogeneous, integral oxide coating within a tubular casing adapted toreceive the said punchings, heat treating the resulting assembly withina temperature range of 650 to 1100 C. in an enveloping gaseousatmosphere obtained by the combustion of hydrocarbon-containing gas in adeficiency of air and containing, by volume, from 3 to 12 per centcarbon monoxide, from 3 to 10 per cent carbon dioxide, from 3 to 25 percent hydrogen and from 0.8 to 3.5 per cent water vapor, the relativeproportions of the said components being such that, at least at themaximum heat-treating temperature, the said gaseous atmosphere isreducing and prevents sticking of the punchings, and at lowertemperatures causes the formation on the surfaces of the encasedpunchings of a continuous, homogeneous, integral, electricallyinsulating oxide coating.

ROBERT T. REARDON.

